Cannot find Background Images feature in Blender 2.8
Background images are gone in Blender 2.8+, at least in the traditional pre-2.7# sense.
The old system was aging and prone to failure as described in the Proposal: Replace background images with Image Empties in 2.8x, and it has been retired due to inherent limitations.
Information was stored as User Interface data, as such if you opened a file without the Load UI option checked they would appear to be missing, when in fact they simply weren't loaded.
Saving the file would then silently erase them, without warning or explicit user intervention leading to permanent data loss.
They were also hard to manipulate and had duplicate functionality, having thus been replaced by more modern and robust solutions.
Alternatives

Either use them as Empties like you could before, if you are using them as reference images to model over. This allows for greater control of size, position and display options.

Use them in the newly added Camera Background feature, if your goal is aligning a camera to an existing photo or matching perspectives, for later compositing a 3D scene over existing footage.

Import them as planes using the Import Images as Planes addon like
in previous versions


Workflow
You can now add most background images in Blender from a dedicated entry in the 3D View &gt; Add &gt; Image menu.

Three options are available if you manually activate the Import Images as Planes addon from Edit &gt; User Preferences &gt; Add-ons &gt; Import Images as Planes). Background and Reference Images are basically different presets for the same underlying tool.

Reference - Act as regular objects, visible from both sides, non renderable



Background - Can be set to display always in front or background, non renderable



Image Plane - Actual renderable mesh with geometry and a material

You can control visibility settings from the Properties Window, like making it visible only for orthographic views, display always in front, adjust transparency and control backface culling for empty based solutions.
You can also use them from the new Camera Background feature, available in the Properties Window &gt; Object Data &gt; Background Images for any currently selected Camera object.

If you require a background image (other than an Image as Plane) to be visible in your render, either set it up a world shader, use a Spherical HDR as an environment map, images as planes for actual geometry, or render with a transparent background and overlay the result over your image through post processing using either the Blender Compositor or any external image editor.